Oscillatory system



April 12, 1938.

Filed Nov. 5, 1935 5/ C T i i lMSl/ZHOR v W WWI/T mumm- FLWUAMEN- gm mm. 741 mm our/w mw 4 HARMO/l/C mm. m

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wsumro/e oar/ ar INVENTQR OBERTS lNSUlATORS WALTER VAN ATTORNEY Patented Apr. 12, 1938 I v UNITED STATES PATENT ()FFICE OSCILLATORY SYSTEM Walter van B. Roberts, Princeton, N. 1., assignor to Radio rp ration of America, a corporation of Delaware Application November 5, 1935, Serial No. 48,306

22 Claims. (01. 250--36) This invention relates broadly to electron disfifty volts, then the impact of the electron on charge device circuits, and particularly to such cathode C will dislodge a. number of secondary circuits which employ devices containing a pair electrons which will now be drawn back toward of cold cathodes or dynodes functioning by means cathode C where they. will arrive half a period of secondary emission of electrons and oppositely (of the fifty megacycle frequency) later, that is, disposed with respect to a central collecting elecwhen C has become positive, thus dislodging a trode. The present invention is especially constill greater number of secondary electrons, cerned with this type of device when used as an which will repeat the process of the first elecoscillation generator, hereinafter referred to as tron. This building up process continues until a double resonance oscillator. the space between electrodes contains so dense 10 In order that the present invention may be a cloud of electrons oscillating back and forth better understood, an explanation will first be that in spite of the constraining magnetic field given of the operation of a double resonance os some of them are pushed over into the anode cillator, with special reference to Fig. 1 of the A, and equilibrium is established when the averaccompanying drawing which illustrates this type I age absorption of electrons by the anode is equal 15 of oscillator. The figure discloses a tube which to the net loss of electrons by secondary emishas an evacuated envelope E enclosing a centralsion from the two electrodes C, C. It will be ly located anode A in the form of a ring, and observed that when one of the cold cathodes C a pair of cold cathodes C, C'.oppositely disposed or C is positive, it suffers a net loss of electrons with respect to the anode A. Cathodes C, C are which constitutes a flow of current between the 20 treated, or specially designed, to emit copious electrode and the resonant circuit contrary in secondary electrons when bombarded by other direction to the flow that would be produced if electrons and are connected to the terminals of the space within the tube were conductive in the a resonant circuit R having an inductance L to ordinary fashion. In other words, the electrodes whose midpoint is connected a battery B which C, 0' present a negative conductance to the ter- 25 maintains the anode A at a positive potential minals of the resonant circuit. As a result of with respect to the cathodes. A coil M surthis, energy is not absorbed from the resonant rounds the envelope for producing a magnetic circuit by the tube, but is actually absorbed by field perpendicular to the plane of the anode. the circuit from the tube. Hence, a tuned cir- In the operation of the double resonance oscuit as shown by R in Fig. 1, if started to os- 30 cillator, an electron free to move in the envelope, cillate sufilciently strong at its natural freproduced by radioactivity, thermal agitation,- quency will continue so to do if it absorbs energy photoelectric effect, or otherwise, will be acfrom the tube faster than it dissipates energy in celerated toward anode A. Assuming that this its own resistance, that is, if the average negafree electron starts from a position near the surtive conductance of the tube measured between 5 face of cathode C, it will travel along the magcathodes C and C exceeds the positive conductnetic lines of force of the field toward C but ance of the tuned circuit R measured at resonant will be prevented by the field from striking ringfrequency between its two ends. It will be oblike anode A. The electron will pass through served that to obtain oscillations the battery B the hole of anode A but will now be decelerated must be adiusted to make the frequency of elec- 40 until it reaches or fails to reach C according to tron oscillation within the tube substantially whether the potential of C is positive or negaequal to the natural frequency of the tuned cirtive. The time required for the electron to travel cuit R, and it is for this reason that such an osfrom C to C is determined by the geometry of cillation generator is herein named a double the tube structure and by the potential of batresonance device. Similarly, throughout this 45 tery B. Assuming that this time is one hundredspecification, the electrodes C, C presenting millionth of a second, and cathodes C, C are exnegative conductance by virtue of secondary cited in opposite phase, either by shock excitaemission will be called dynodes, following the tion of the tuned circuit R or by an external alnomenclature of A. W. Hull who first produced ternating frequency source coupled to R, with a negative conductance by means of secondary voltage whose frequency is fifty-million cycles emission. per second and with an amplitude of fifty volts An object of the present invention is to provide on each cathode, and that the electron previously an improved double resonance oscillator for very considered arrives at C at a moment when the short wave lengths. potential of C'- is positive and something like A furtherobject of the invention is to provide 55 an electron discharge device for generating short waves having a vacuum tight envelope which also acts as the oscillatory circuit of the oscillator.

A still further object is to provide an oscillatory circuit for the generation of short waves having portions thereof acting also as dynode electrodes of an electron discharge device.

According to the present invention, the resonant circuit is replaced by a tank or oscillatory circuit in the form of an evacuated metallic container having distributed inductance and capacity. This tank or oscillatory circuit is provided with a pair of inwardly projecting tubes or cylinders whose inner confronting surfaces are treated to act as dynodes.

,In the accompanying drawing:

Fig. 1 illustrates diagrammatically a double resonance oscillator, given merely for the purpose of the foregoing exposition, and

Figs. 2, 3, 4, and illustrate different embodiments of the invention.

Referring to Figs. 2 and 3 in more detail, there are shown double resonance oscillators functioning broadly on the principle outlined in connection with the system of Fig. 1. In Fig. 2 the oscillatory tank circuit comprises a metallic evacuated sphere D having inwardly projecting tubes T, T whose inner confronting cold surfaces C, C acting as cathodes or dynodes are oppositely disposed with respect to a centrally located anode A in the form of a ring. These dynodes are treated, or specially designed, to emit copious secondary electrons when bombarded by other electrons. The path for electrical oscillations is then from the end of an inwardly projecting tube, let us say T, out to the sphere D, around the sphere, and back in to the inner end of the other inwardly projecting tube T. The ends of these inwardly projecting tubes are closed and form the dynodes for electron discharge phenomena exactly as shown in Fig. 1. Similarly as in Fig. l, a collector ring anode A is maintained at a high positive potential by a battery B and brought out through the sphere D by way of a glass bead seal F. This seal is located in the plane of the collector ring which is a plane of neutral radio frequency potential on the sphere. The negative end of the battery B is connected to a point in this neutral plane, pref erably close to the seal. In the drawing the ground connection G is shown a little off the neutral plane for the sake of simplicity of illustration, although in practice it is located directly behind the seal F.

Inside the hollow inwardly projecting tubes are located rods of high magnetic permeability forming pole pieces N and S for providing the magnetic circuit shown. If desired, permanent bar magnets may be used instead. In either case, the desired magnetic field between the dynodes C, C which is substantially parallel to the axis of the collector A is produced, as shown by the dotted lines. If oscillations of an even harmonic frequency are desired, such oscillations may be taken off to a utilization circuit by way of transformer TR. Due to the opposing eflect of the inner part of the oscillatory tank. circuit, there will not be much potential drop along the sphere, but the finite spacing prevents complete neutralization at very high frequencies and there is also some drop due to the resistance of the sphere D, so that a certain amount of voltage is produced. Oscillations of fundamental frequency may be obtained from ground and a point P on the sphere D other than in the neutral plane, the distance from the neutral plane where the connection to the sphere is made depending upon the impedance of the output circuit to be energized. Balanced output may be taken between two such points on either side of the neutral plane. Larger voltages may be obtained by connecting to points within the sphere. For instance, balanced output may be obtained between points P', P' on the vacuum surface of tubes T, T of the sphere symmetrically located with respect to the neutral plane by way of lecher wires, as shown.

Sphere D and cylinder tubes T, T are made of low resistance metal such as copper, and the surfaces thereof toward the vacuum is made to be as smooth as possible, inasmuch as it is this surface that carries the greatest-current density.

Fig. 3 shows a modification of Fig. 2 wherein the sphere D has been flattened down to form a cylinder D. The magnetic field may be provided exactly as in Fig. 2, or, alternatively, a field coil M may be wound around. the entire structure as shown. In this figure an alternative method for taking off energy at an even harmonic frequency is shown consisting of direct connections from ground and a point X on the lead connecting the collector A to the battery B, the distance along the anode lead depending upon the load impedance. At high frequencies this lead has sufficient impedance to produce a voltage drop of appreciable magnitude. A blocking condenser N is shown in the output connection to the anode lead. For fundamental frequency output or take-off, the load may be connected between the neutral plane and another point on the external cylinder, or between sy metrically located points, in similar fashion to the methods described in connection with Fig. 2.

By substituting a grid like element for the collection ring A, as shown in Figs. 4 and 5, more fully described in copending application Serial No. 46,980, filed October 28, 1935, by applicant and Charles H. Brown, the magnetic field may be dispensed with.

In Fig. 4, the usual ring anode is here replaced by a screen or perforated plate PL, and the dynodes C, C are surrounded by guard rings GR, GR maintained at a suitable potential, pref erably somewhere near the average potential of the dynodes, by variable battery VB, so that the lines of electrostatic force from the dynodes C, C to the collector anode PL are substantially parallel. Screen node PL presents an area of solid matter which is so small relative to the area of the perforations that the collector PL will receive (prior to the time when any siderable space charge is built up withiitube) a lesser proportion of electrons oas':.:lg therethrough than the ratio of gain of 6....31110115 at each impact to the number before impact. That is, if we consider a certain number of electrons about to strike the right hand dynode C, the collector PL must not receive as much as the total increase in number when the secondary electrons come back through it, otherwise the number of electrons oscillating within the tube would not build up. Best results will be obtained by using extremely fine wires for the collector electrode PL and making the mesh as coarse as possible without upsetting the uniformity of the electrical field in the space between collector PL and dynodes C, C.

In Fig. 5. the dynodes or cathodes C, C extend, as a surface which is somewhat spherical,

1 arounda small fine grid structure G, which may even be a single wire. The dotted lines indicate the paths of the electrons which are not now parallel as in the previous structures 'of Figs. 1 to 4, inclusive. The featureof Fig. 5. is that the lengths of the paths of electrons from one dynode C to the other dynode Clare approximately the same, although there is a wide variety of these paths. v

It will be understood, of course, that the invention is not limited to the precise details described in connection with the drawing since various modifications may be made without departing from the spirit and scope of the invention. The oscillator of the invention can be used in receivers as well as in transmitters, and in circuits similar to the manner of otherknown types of electron discharge device oscillation generators.

What is claimed is:

1. An electron discharge device comprising an evacuated metallic envelope constituting an oscillatory circuit and containing an inwardlyprojecting portion, the end of said inwardly projecting portion presenting a surface capable of emitting secondary electrons on impact of a primary electron, an electron collector element located between said surface and the surface of the envelope opposite thereto, and. means for applying a positive potential to said collector element with respect to said surfaces.

2. Apparatus in accordance with claim 1 char acterized in this that said collector element is in the form of a ring in a plane perpendicular to the path of travel of the electrons between said surfaces, thus presenting an unobstructed space for movement of electrons between said surfaces.

3. An electron discharge device comprising a metallic envelope containing an inwardly projecting portion, the end of said inwardly projecting portion and the portion of the envelope opposite said end presenting cold surfacesv capable of emitting secondary electrons on impact of a primary electron, an electron collector element 10.

cated between said surfaces and in a plane substantially perpendicular to the path of travel of the electrons between said surfaces, means for applying a positive potential to said collector element with respect to said surfaces, and means for applying a magnetic field between said surfaces which is perpendicular to the plane of said element.

4. In combination, an electron discharge device comprising an evacuated metallic envelope comprising as a part thereof a pair of surfaces capable of emitting electrons on impact, an element located substantially midway between said surfaces which element enables the passage of electrons between said surfaces, and a source of energy for maintaining said element at a positive potential with respect to said surfaces.

5. Apparatus in accordance with claim 4, characterized in this that said element is a grid.

6. In combination, an electron discharge device comprising a metallic envelope containing two oppositely disposed inwardly projecting portions, the confronting surfaces of which are capable of emitting secondary electrons on impact, an element located between said surfaces which enables the passage of electrons therebetween, and a site said end I presenting surfaces capable of emitting secondary electrons on impact of a primary electron, an anode located between said surfaces, means for applying a positive potential to said anode with respect to said surfaces, and a coil surrounding said envelope for producing a magnetic field perpendicular to the plane of said anode.

8. An electron discharge device comprising a metallic envelope containing an inwardly projecting portion, the end of said inwardly projecting portion and the portion of the envelope opposite said end presenting surfaces capable of emitting secondary electrons on impact of a primary electron, an anode located between said surfaces, means for applying a positive potential to said anode with respect to said surfaces, and

'vice comprising an evacuated metallic envelope comprising as a part thereof a pair of surfaces capable of emitting electrons on impact, an element located between said surfaces which enables the passage of electrons between said surfaces, a source of energy for maintaining said element at a positive potential with respect to said surfaces, and means for applying a field which is perpendicular to the plane of said element.

10. In combination, an electron discharge device comprising an evacuated metallic envelope comprising as a part thereof a pair of surfaces capable of emitting electrons on impact, an element located between said surfaces which enables the passage of electrons between said surfaces, an external source of energy, a connection from said element to the positive terminal of said source, a connection from said envelope to the negative terminal of said source, means for insu-- lating said first connection from said envelope, and an output circuit coupled to said first connection.

11. In combination, an electron discharge device comprising a metallic envelope containing two oppositely disposed inwardly projecting portions, the confronting surfaces of which are capable of emitting secondary electrons on impact, an element located between said surfaces which enables the passage of electrons therebetween, a source of energy for maintaining said element at a positive potential with respect to saidsurfaces, and an output circuit comprising a pair of connections in contact with said inwardly projecting portions. r

12. Apparatus in accordance with claim 11,

characterized in this that said pair of connections are lecher wires adjustable over said projections and extending from within said container externally thereof, said lecher'wires being '13. Apparatus in accordance with claim 1, 7

characterized in this that said metallic envelope is in the form of a sphere, except for the inwardly projecting portion.

14. In combination, an electron discharge device comprising a metallic envelope containing two oppositely disposed inwardly projecting portions, the confronting surfaces of which are capable of emitting secondary electrons on impact, an element located between said surfaces which enables the passage of electrons therebetween, a guard ring surrounding the periphery of each surface for producing lines of electrostatic force which are substantially parallel from the surfaces to the element, and a source of energy for maintaining said element at a positive potential with respect to said surfaces and guard rings.

15. In combination, an electron discharge device oscillator comprising an evacuated metallic envelope comprising as a part thereof a pair of cold surfaces capable of emitting electrons on impact, an element located between said surfaces which enables the passage of electrons between said surfaces, a source of energy for maintaining said element at a positive potential with respect to said surfaces, and means for obtaining output energy from said oscillator.

16. In combination, an electron discharge tievice comprising a metallic envelope containing two oppositely disposed inwardly projecting portions, the confronting surfaces of which are capable of emitting secondary electrons on impact, said surfaces being substantially spherical in form, a grid located between said surfaces, and a source of energy connected to said grid for maintaining same at a positive potential with respect tosaid surfaces.

1'1. An electron discharge device comprising an enclosed metallic envelope constituting an oscillatory circuit having therein as part of said envelope, a pair of cold electron emitting electrodes adapted to maintain oscillations in said circuit, said cold electrodes being treated to produce copious secondary electrons upon impact with other electrons, and an electron collecting element located between said electrodes.

18. An electron discharge device comprising an evacuated metallic envelope constituting an oscillatory circuit and containing an inwardly projecting portion, the end of said inwardly projecting portion presenting a surface capable of emitting secondary electrons on impact of a primary electron, an electron collector element in the form of a planar grid located substantially midway between said surface and the surface of the envelope opposite thereto, said grid being in a plane substantially perpendicular to the path of travel of the electrons between said surfaces, and means for applying a positive potential to said collector element with respect to said surfaces.

19. An electron discharge device comprising a metallic envelope containing an inwardly projecting portion, the end of said inwardly projecting portion and the portion of the envelope opposite said end presenting cold surfaces capable of emitting secondary electrons on impact of a primary electron, an electron collector element located substantially midway between said surfaces and in a plane substantially perpendicular to the path of travel of the electrons between said surfaces, means for applying a positive potential to said collector element with respect to said surfaces, and means for applying a magnetic field between said surfaces which is perpendicular to the plane of said element.

20. In combination, an electron discharge device comprising an evacuated metallic envelope comprising as a part thereof a pair of surfaces capable of emitting electrons on impact, an electron collecting element located substantially midway between said surfaces, said element being in a plane substantially perpendicular to the path of travel of electrons between said surfaces, and a source of energy for maintaining said element at a positive potential with respect to said surface. 1

21. In combination, an electrondischarge device comprising an evacuated metallic envelope comprising as a part thereof a pair of surfaces capable of emitting electrons on impact, an electron collecting element located substantially in the center of said envelope and between said surfaces which enables the passage of electrons between said surfaces, an external source of energy and a connection from said element to the positive terminal of said source, a conne'ctionfrom said envelope to the negative terminal of said source, means for insulating said first connection from said envelope, and an output circuit coupled to said first connection.

22. An electron discharge device comprising an enclosed metallic envelope constituting an oscillatory circuit and having as part thereof a pair of cold electron emitting electrodes, said cold electrodes being treated to emit copious secondary electrons upon impact with other electrons, and an electron collecting element located substantially midway between said electrodes and in a plane substantially perpendicular to the path of travel of the electrons.

WALTER van B. ROBERTS. 

